Republicans buoyantly forecast a new era of divided government, two years after Democrats sealed victory in the presidency, the House and the Senate and set about reshaping the agenda in a time of severe recession and war. Democrats did not seriously dispute expectations that they would lose the House this time, even while campaigning through the final hours to stem losses.
His campaign travels over, Obama was taping interviews with radio hosts in Milwaukee, Cincinnati, Philadelphia, Honolulu and Miami as well as one with Ryan Seacrest of "American Idol" for his national radio show, all for broadcast Tuesday as Americans vote. In one interview he pulled back from earlier remarks calling Republicans "enemies" of Hispanics.
Democrats tend to be strong closers, with a vaunted operation by the party, Obama's organizers and unions to get supporters to voting sites on Election Day. This time, they faced a ground game infused by the tea party, less polished than the other side but full of energy.
The midterm elections are a prime-time test for that loosely knit and largely leaderless coalition, a force unheard of just two years ago. Tea party supporters rattled the Republican establishment in the primaries, booting out several veteran lawmakers and installing more than 70 candidates, nearly three dozen of whom are in competitive races Tuesday.
If successful, that conservative movement could come to Washington as a firewall against expansive federal spending, immigration liberalization and more, as well as a further threat to the historic health care law that Republicans hope somehow to roll back.
In Thornton, Colo., on Monday, coffee and leftover Halloween candy fueled volunteers at campaign offices of both Senate candidates, Democratic incumbent Michael Bennet and Republican Ken Buck. Republican helper Susan Nalbone, 55, a retired schoolteacher who was phoning voters, said her side was dispirited in 2008. Not now.
"This is more intense," she said. "I know that elections are all important, all a big deal, but this one feels especially important to people."
At Bennet's office, LuAnn Lind, 52, a nurse, said she's been volunteering for Democrats for years and finding it harder now to fire people up. "It's a little less urgent among the people I'm talking to," Lind said. "I'm telling them: 'We don't want to lose ground now. We want to keep the Obama momentum moving forward.'"
Ohio Rep. John Boehner, in line to become speaker if Republicans win the House, promised Monday to hold weekly votes to cut federal spending, make jobs the top GOP priority and fight to repeal the health law. Former President Bill Clinton, campaigning for Democrats as if his own future were on the line, stumped late into the night in New York, Pennsylvania, West Virginia, Kentucky and Florida.
Republicans need 40 more seats to win the House, a goal that polls indicated they might achieve. Races for more than 100 of the 435 seats are competitive.
Republicans need a net gain of 10 to take the Senate, a tougher road that requires them to win every tight race. The GOP also made strong bids to add governors to their ranks and expand in state legislatures.
Voter mobilization efforts have been unfolding for weeks as more than 14 million Americans cast early ballots.
In Nevada, home of the hot Senate contest between Democratic Majority Leader Harry Reid and tea-party pick Sharron Angle, registered Democrats and Republicans came out early in similar numbers. In Pennsylvania, another battleground, more than half the early voters were Republican, by the latest count.
"I need you in the next few hours," Reid told supporters at a rally Monday with first lady Michelle Obama. "Don't hope someone else will work harder than you. You need to knock on that extra door. You need to make that extra phone call."
Some races could go days or more without a winner, thanks to the multitude of expected close contests - in Colorado, Nevada, Illinois, West Virginia, Ohio, Alaska and more - and the persistence of shaky voting systems in some places a decade after the presidential-election counting disaster in Florida.
Hundreds of lawyers from both sides are ready to roll. This was a campaign marked by the ragged anger of partisans and caustic ads by candidates, now spilling into an Election Day that's likely to lead to complaints of voting irregularities, fraud or machine meltdowns - and hair-trigger legal challenges.
One of the most unpredictable races was unfolding in Alaska, where Sen. Lisa Murkowski, upset in the GOP primaries by the tea party's pick, Joe Miller, is trying to win by having voters write her name on the ballot. Democrats injected cash late in the campaign to try to lift their candidate, Scott McAdams, over the other two.
Voters in 37 states are electing governors. Among the most competitive: the contest in Ohio between Democratic Gov. Ted Strickland and former Republican Rep. John Kasich.
AP writers Kristen Wyatt in Thornton, Colo., and Michael R. Blood and Cristina Silva in Las Vegas contributed to this report.